fn main() {
    let k = read::<i64>();
    if k == 0 {
        println!("{}", std::f64::consts::PI * std::f64::consts::PI / 6.0);
        return;
    }
    let mut ans = 0.0;
    for i in 1..k + 1 {
        ans += 1.0 / k as f64 / i as f64;
    }
    println!("{}", ans);
}

fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}